The present invention relates to a thermal transfer recording apparatus and method for thermal transfer recording for transferring and recording thermal transfer recording material of a thermal transfer recording medium on a printing medium utilizing heat generation of a heat generating element of a line type thermal head.
With regard to a thermal transfer recording apparatus, for example, it is known in Jpn. Pat. Appln. KOKAI Publication No. 59-188452. As shown in FIG. 16, it comprises print units 101, 102, 103 and 104 of yellow, magenta, cyan and black, respectively, which are disposed in this order along a straight conveyance path 106 for a printing medium 105.
The print unit 101 for yellow includes a line type print head 101-1 utilizing a thermal head, a thermal transfer recording mechanism having spools 101-3 for supplying an yellow ribbon as a thermal transfer recording medium 101-2 including yellow ink over a heating face of a heat generating element constituting the line type print head 101-1 and a transfer pressure roller 101-4.
The other print units 102 to 104 have the exactly same structure as the yellow print unit 101 described above except the color to be used for thermal transfer recording medium, i.e., magenta, cyan and black, respectively; and comprise line type print head 102-1, 103-1 and 104-1, respectively, thermal transfer recording mechanism having spools 102-3, 103-3, 104-3, respectively, for supplying the thermal transfer recording medium 102-2, 103-2, 104-2, respectively, over the heating face of the heat generating element constituting the line type print head, respectively, and the transfer pressure roller, respectively.
It is arranged that a printing medium 105 is conveyed from the feed rollers 107 and the yellow print unit 101 toward the black print unit 104 on the conveyance path 106 and among each print 101 to 104, and it passes through between the thermal recording media 101-2 to 104-2 and the transfer pressure rollers 101-4 to 104-4.
When carrying out recording, while conveying the printing medium 105 from the yellow print unit 101 through to the black print unit 104, yellow is transferred first at the yellow print unit 104. When the transferred portion comes to the heating face of each print head 102-1 to 104-1 on each print unit 102 to 104, each color is transferred synchronously overlapping in order. At this time, colors are overlapped and mixed, thus it is made possible to record a desired hue.
As described hereinbefore, in a thermal transfer recording in which three or four print units are provided and each print head prints a specific color, different from a method in which only one print head prints a plurality of colors, as a printing medium 105 is not reciprocally conveyed frequently, it is made possible to carry out a high speed recording.
Also, in Jpn. Pat. Appln. KOKAI Publication No. 10-226178, it is disclosed that a thermal transfer recording medium of which dynamic modulus of elasticity at 70xc2x0 C. is 1xc3x97106 to 1xc3x971010 in order to form a recorded image excellent in abrasion resistance and heat resistance using a line type thermal head.
Further, in Jpn. Pat. Appln. KOKAI Publication No. 8-52942, it is disclosed that a thermal transfer recording medium of which loss tangent tan xcex4 measured by viscoelasticity measurement of ink layer at 60xc2x0 C. to 100xc2x0 C. is within a range of 0.4 to 2.5 is used in order to make a clear thermal transfer recording on a plan medium to be transferred at a low cost.
Furthermore, in a thermal transfer recording apparatus utilizing a serial type thermal head, for example, a thermal transfer recording medium is pressed to bring the same into contact with a printing medium with a large line pressure of approximately 2.0 N/mm. Line pressure means load per unit length in the direction of the arrangement of the heat generating elements. It is known that even when the smoothness of the surface of the printing medium is low (coarse), unevenness of the surface is made smooth and the adhesiveness of the thermal transfer recording medium is increased. Further, in a thermal transfer recording apparatus utilizing a serial type thermal head, thermal transfer recording medium such as an ink ribbon is narrow in width and it is made possible to be compact in size and to be stored in a cassette. As a result, it provides an advantage that wrinkles are hardly generated on the thermal transfer recording medium even when a relatively large line pressure is given thereto.
Whereas, in a line type thermal head mounted with a line type thermal head, a line type thermal transfer recording medium was prepared utilizing the same technique as that for conventional thermal transfer recording medium, and the thermal transfer recording material in a softened or melted status by a heat from a thermal head was peeled off from the thermal transfer recording medium before it cooled down to a room temperature to a printing medium under conveyance, of which smoothness of the surface is low (coarse). As a result the following problems were found, i.e., ink was not transferred well onto the unevenness on the surface of the printing medium, and it was unstable; the edge of the recorded image was not sharp but zigzag resulting in a low quality of the recorded image. However, when a recorded image is required a dimensional accuracy, or when a high resolution recorded image is required, for example, bar code or OCR (Optical Character Recognition) etc which carry out reading process of a recorded image information with an optical means after recording, quality of the edge becomes essential. Still further, when a color recording in which a plurality of thermal transfer recording materials of different colors are transferred overlapping in order, due to not only smoothness of the surface of a printing medium but also the thermal transfer recording material of the thermal transfer recording medium previously transferred thereto, the edge of the recorded image may become zigzag. A problem is that desired recorded image can not be obtained.
Furthermore, another problem is: when a large line pressure is given to a line type thermal head same as a serial type thermal head used in a thermal transfer recording apparatus in order to increase the adhesiveness between the thermal transfer recording material of a thermal transfer recording medium and a printing medium, as the width of the thermal transfer recording medium is wider than that of the serial type, it is difficult to apply an even line pressure over the full width of the thermal transfer recording medium. As a result, wrinkles are easily generated resulting in a low quality of the recorded image.
As described hereinbefore, such problems exist that, when a thermal transfer recording material in a softened or melted status by a heat from the heat generating elements on a line type thermal head is peeled off from the supporting material of the thermal transfer recording medium and transferred to a printing medium under conveyance before it cools down to a room temperature, if the line pressure of the head is increased, wrinkles are generated; while if the line pressure is reduced to prevent the wrinkles from being generated, it causes an unstable transfer and a high quality recorded image can not be obtained.
An object of the present invention is to provided a thermal transfer printing apparatus utilizing a line type thermal head provided with a plurality of heat generating elements disposed thereon, which enables to obtain a high quality recorded image with sharp edges.
Another object of the present invention is to provided a method for thermal transfer printing utilizing a line type thermal head provided with a plurality of heat generating elements disposed thereon, which enables to obtain a high quality recorded image with sharp edges.
In accordance with the present invention, a thermal transfer recording apparatus comprises a line type thermal head provided with a plurality of heat generating elements disposed thereon; a thermal transfer recording medium formed with thermal transfer recording material over a supporting material, of which dynamic shear modulus of elasticity is within a range of 1xc3x97103 Pa to 8xc3x97105 Pa, and loss tangent tan xcex4 is within a range of 0.6 to 2.5 measured in dynamic viscoelasticity measurement in a temperature range of the melting point thereof to 50xc2x0 C. over the same at a frequency of 0.5 Hz; first conveyance means for conveying a printing medium; second conveyance means for conveying each heat transfer recording medium; pressure contact means for pressurizing the heat generating elements against the thermal transfer recording medium to bring the same into contact therewith with a load of 0.3 to 1.0 N/mm, which is load per unit length in the direction of the arrangement of the heat generating elements; and transfer means for transferring the thermal transfer recording medium to the printing medium by heating each heat generating element of the line type thermal head when carrying out a recording and by peeling off the same in a softened or melted status from the supporting material thereof.
In accordance with the present invention, a method for thermal transfer recording to transfer a thermal transfer recording material from a thermal transfer recording medium to a printing medium to make a printing by heating each heat generating element of a line type thermal head provided with a plurality of heat generating elements disposed thereon, comprises the steps of utilizing a thermal transfer recording material of which dynamic shear modulus of elasticity is within a range of 1xc3x97103 Pa to 8xc3x97105 Pa, and loss tangent tan b is within a range of 0.6 to 2.5 measured in dynamic viscoelasticity measurement in a temperature range of the melting point thereof to 50xc2x0 C. over the same at a frequency of 0.5 Hz; pressurizing heat generating elements on the line type thermal head against the thermal transfer recording medium to bring the same into contact therewith with a load of 0.3 to 1.0 N/mm, which is load per length in the direction of the arrangement of the heat generating elements as well as transferring the thermal transfer recording material to the printing medium by peeling off the same in a softened or melted status from the supporting material thereof.
Further, in accordance with the present invention, it is made possible to provide a thermal transfer recording apparatus which enables to obtain a high quality recorded image with sharp edges stably on a printing medium with coarse surface under conveyance by utilizing a line type thermal head of which line pressure does not generate wrinkles on a thermal transfer recording medium, and by utilizing a thermal transfer recording material of the thermal transfer recording medium having a specific dynamic shear modulus of elasticity and loss tangent tan xcex4 characteristic in order to peel off the thermal transfer recording material in a softened or melted status from the supporting material of the thermal transfer recording medium and to transfer to a printing medium.
Further, in accordance with the present invention, it is made possible to provide a method for thermal transfer recording, which enables to obtain a high quality recorded image with sharp edges stably on a printing medium with coarse surface under conveyance by utilizing a line type thermal head of which line pressure does not generate wrinkles on a thermal transfer recording medium, and by utilizing a thermal transfer recording material of the thermal transfer recording medium having a specific dynamic shear modulus of elasticity and loss tangent tan xcex4 characteristic in order to peel off the thermal transfer recording material in a softened or melted status from the supporting material of the thermal transfer recording medium and to transfer to a printing medium.
Still further, in accordance with the present invention, it is made possible to provide a method for thermal transfer recording, which enables to obtain a high quality recorded image with sharp edges without being influenced by the smoothness of the surface of a printing medium and/or the thermal transfer recording material previously transferred on the thermal transfer recording medium even when carrying out a color recording by transferring a plurality of thermal transfer recording material of different colors overlapping in order.
As described hereinbefore, it is very effective for recording an image which is required dimensional accuracy of the record or for recording a high resolution image.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.